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Thursday, 31 May 2012

Is This the Key to Vastly Better Batteries?

Power maker: This component is part of a new, cheaper process
to make ionic liquids (upper left) that could greatly boost the storage
capacity of batteries.
Credit: Boulder Ionics

Researchers are experimenting with a handful of ideas that could make batteries vastly better than they are today, which could lead to more affordable electric cars and cheaper ways to store solar power to use at night. But many of these approaches have one thing in common: they aren't practical because of the shortcomings of existing battery electrolytes.

Jerry Martin, CEO and cofounder of a small startup in Colorado, says his company—Boulder Ionics—is developing a way of making a type of electrolyte that would enable high-performance batteries. The electrolyte, made from ionic liquids—salts that are molten below 100 ⁰C—can operate at high voltages and temperatures, isn't flammable, and doesn't evaporate. Ionic liquids are normally expensive to produce, but Boulder Ionics is developing a cheaper manufacturing process.

Replacing conventional electrolytes with ionic liquids could double the energy storage capacity of ultracapacitors by allowing them to be charged to higher voltages. That could make it possible to replace a starter battery in a car with a battery the size of a flashlight, Martin says.

The electrolytes could also help improve the storage capacity of lithium-ion batteries, the kind used in electric vehicles and mobile phones; and they could help make rechargeable metal-air batteries practical. In theory, such batteries could store 10 times as much energy as conventional lithium-ion batteries.

Boulder Ionics, which is a year-and-a-half old, has built and demonstrated the key pieces of equipment needed for its process and used them to make evaluation samples for battery manufacturers. Earlier this year, it raised $4.3 million in venture capital.

Martin says his company's process could actually make ionic liquids that are cheaper than conventional electrolytes per watt-hour of energy storage in the batteries they enable.

The company is reducing the cost of making them in two main ways. First, it's switching from a batch process to a continuous one. This is far faster—it takes six minutes to make ionic liquid electrolyte, compared to three days for a conventional process—and allows the company to produce more material with a given-size piece of equipment, which reduces capital costs. Instead of building a large chemical plant, it would be possible to make enough ionic liquid for 100,000 electric cars in a space the size of a living room, Martin says.

The continuous process also gives Boulder Ionics more precise control over the chemical reactions involved, which reduces impurities. Martin says this makes costly purification steps unnecessary. Scaling up continuous production could prove a challenge, however.

For use in ultracapacitors, the new ionic liquid electrolyte can simply replace a conventional one. "It's a nearly drop-in replacement, compatible with existing production lines," Martin says. But battery makers will need to switch to new electrode materials that operate at higher voltages to take advantage of the high-voltage resistance of ionic liquids in lithium-ion batteries.

Ionic liquids are suitable for rechargeable metal-air batteries because the electrolyte in such a battery is exposed to the air, and ionic liquids do not evaporate. At least one company, Fluidic Energy, is hoping to make metal-air batteries practical by using ionic liquids.